Andrew Dunstan wrote:
I've been reading over the documentation to find an alternative to
the deprecated xpath_table functionality. I think it may be a
possibility but I'm not seeing a clear alternative.
Thanks,
Chris Graner
The standard is XMLTABLE and is implemented by both db2 and oracle but
is on our list of unimplemented features. I would love to see this
implemented in Postgres. I recall it coming up here before. But I
don't think it went beyond discussing which xquery library we could use.
Yes, Chris spoke to me about this last night and emailed me an example
of what he needs today, and I've spent the couple of hours thinking
about it. Not have a nice way of getting a recordset out of a piece of
XML is actually quite a gap in our API.
The trouble is that XMLTABLE is a horrible grammatical mess, ISTM, and I
don't much like the way xpath_table() works either. Passing a table name
as text into a function is rather ugly.
I think we could do with a much simple, albeit non-standard, API.
Something like:
xpathtable(source xml, rootnodes text, leaves variadic text[])
returns setof record
But unless I'm mistaken we'd need the proposed LATERAL extension to make
it iterate nicely over a table. Then we could possibly do something like:
select x.bar, x.blurfl
from
foo f,
lateral
xpathtable(f.xmlfield,'//foo','bar','baz[1]/blurfl','@is-some-property')
as x(bar int, blurfl text, xmlprop bool)
where f.otherfield or x.xmlprop;
cheers
andrew
I agree that the syntax of XMLTABLE is odd. But not demonstrably worse
than xpathtable. If we are going to exert effort on it, why not do it in
a standards compliant way? Otherwise I'd suggest a stop gap of just
adding some support functions to make it easier to extract a scalar
value from a node. Something like what I did here.
http://scottrbailey.wordpress.com/2009/06/19/xml-parsing-postgres/
The nice thing about XMLTABLE is that it adds xquery support. I think
the majority of xquery engines seem to be written in Java. XQuilla is
C++. I'm not sure if our licensing is compatible, but it I would love
the irony of using Berkeley DB XML (formerly Sleepycat) now that its
owned by Oracle.
Scott
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